1. Field of the Invention
The present invention relates to molds and molded articles for forming molded plastic articles which can be used as an oil or air filter used in a car or electronic equipment, a filter used in daily necessities including kitchen utensils and articles used in a bathroom or a toilet, and various filters used for straining, draining and other various purposes, and more particularly, to a molding apparatus which is suitable for molding a fine net filter.
2. Description of Related Art
Conventionally, molded plastic articles such as a net plastic filter having a frame were produced by an insert molding instead of an one-piece molding in order to avoid difficulties in molding. However, the insert molding demands too many processes and high cost. In performing the insert molding, bonding of a meshed net to the frame is important. This reduces the yield. Thus, strict test processes are required. Attempts at one-piece molding encountered the following drawbacks.
(1) If molten resin is injected into net rib grooves at a low injection pressure, the molten resin can not reach to the end of the grooves due to lack of injection pressure and it is likely that there would be some of the net ribs missing or some parts of the plate distorted especially at distant locations from a gate. PA1 (2) If a high pressure injection is applied, there would be no ribs missing or plate distortion. But, in the case of net ribs, the space between the ribs would be closed, resulting in the possibility of failing to serve as a filter or a net. Further, regulation of the pressure is complicated. If the molten resin flows into a mold within the range of a diameter of a gate of 0.8 to 0.2 .phi., the resin is compelled to flow into latticed grooves that are too fine. In this case, the following drawbacks are caused. PA1 (3) To improve flowability, it is necessary to increase the temperature of the molten resin. Thus, since gas or air produced from hot molten resin might stay within the mold, the molten resin could not uniformly reach to the end of the fine grooves even under the sufficiently high injection pressure. PA1 (4) Further, to improve flowability, it is necessary to make the injection pressure higher. This requires a large-sized molding apparatus. It is impossible for a low cost molding apparatus to be employed. PA1 (5) Further, since it is necessary to increase the temperature of the resin to improve flowability, it is necessary to employ a hot runner of high cost and significantly increase the temperature of the mold. PA1 (1) providing a mold structure which can provide generally uniform flow of the molten resin. PA1 (2) providing a mold structure which can improve flowability of the molten resin. PA1 (3) providing a mold structure which can improve flowability of the molten resin and can prevent missing ribs at the point to which the molten resin has difficulty reaching or moldings defect in the thick portions. PA1 (a) a net groove formed at the upper mold and/or the lower mold, said net groove comprising fine grooves extending in a vertical and/or horizontal directions; PA1 (b) a passage groove having a large diameter or a large width, for facilitating the entrance of the molten resin, the passage groove being formed on the net groove of the upper mold and/or the lower mold; PA1 (c) at least one pin point gate formed on the passage groove to inject the molten resin into the mold, having a diameter of 1.5 .phi. or more to be suitable for the shape or size of the plastic article; and PA1 (d) a frame groove formed to surround the net groove in the upper mold and/or the lower mold. PA1 (a) a net groove formed at the upper mold and/or the lower mold, said net groove comprising fine grooves extending in a vertical and/or horizontal directions; PA1 (b) a passage groove having a large diameter or a large width, for facilitating the entrance of the molten resin, the passage groove being formed on the net groove of the upper mold and/or the lower mold; PA1 (c) at least one gate formed on the passage groove, for injecting the molten resin into the mold; PA1 (d) a frame groove formed to surround the net groove in the upper mold and/or the lower mold; and PA1 (e) a band-shaped groove protrudes to communicate with the frame groove in a direction toward the gate from the frame groove, the depth of which being gradually formed to be low toward the center of the mold. PA1 (a) a net groove formed at the upper mold and/or the lower mold, said net groove comprising fine grooves extending in a vertical and/or horizontal directions; PA1 (b) a passage groove having a large diameter or a large width, for facilitating the entrance of the molten resin, the passage groove being formed on the net groove of the upper mold and/or the lower mold; PA1 (c) at least one gate formed on the passage groove, for injecting the molten resin into the mold; PA1 (d) a frame groove formed to surround the net groove in the upper mold and/or the lower mold; and PA1 (e) a plurality of guide grooves having a large diameter or a large width, both ends of which are not directly connected to the frame groove, formed in rectangular or cross-rectangular direction, in order that the molten resin injected into the mold through the gate can enter into the fine groove after the pressure of the molten resin is accumulated. PA1 (a) a net groove formed at the upper mold and/or the lower mold said net groove comprising fine grooves extending in a vertical and/or horizontal directions; PA1 (b) a passage groove having a large diameter or a large width, for facilitating the entrance of the molten resin, the passage groove being formed only in one direction on the net groove of the upper mold and/or the lower mold; PA1 (c) at least one gate formed on the passage groove, for injecting the molten resin into the mold; and PA1 (d) a frame groove formed to surround the net groove in the upper mold and/or the lower mold. PA1 (a) a net groove formed at the upper mold and/or the lower mold, said net groove comprising fine grooves extending in a vertical and/or horizontal directions; PA1 (b) a passage groove having a large diameter or a large width, for facilitating the entrance of the molten resin, the passage groove being formed on the net groove of the upper mold and/or the lower mold; PA1 (c) at least one gate formed on the passage groove, for injecting the molten resin into the mold; and PA1 (d) a frame groove formed to surround the net groove in the upper mold and/or the lower mold.
In order to solve the drawbacks (1) to (5), the applicant of this invention has already suggested an improved plastic filter having a guide or an improved mold having a guide groove in the following: Japanese Patent Publication No. Hei 7(1995)-20677, Japanese Non-examined Patent Publication Nos. Hei 6(1994)-126784, 6(1994)-15531, 7(1995)-52164, 7(1995)-137166 and 7(1995)-284617.
However, further study is necessary to obtain perfectly molded articles having good plasticity and yield without any defect such as burrs or welds.
Therefore, it is intended in the present invention that a diameter of a gate, which is typically 0.8 to 1.5 .phi. in performing molding in a pin point gate, is 1.5 .phi. or more for low injection pressure and high temperature of the molten resin with halting gas or air. If the diameter of the pin point gate becomes large, a gate cut is essentially required. For this reason, the diameter should be maintained within the range of 1.2 .phi.. However, since the temperature difference between a gate part and a molded article part is large in net articles in which the molded article part is not likely to regenerate, a net filter does not require the gate cut even if the diameter of the gate becomes larger.
In the prior art, there is a direct gate method used for molding a plastic basket or a thin frame box article in the case of a gate having a large diameter. However, this direct gate method requires a gate cut process later.
There are a number of problems to be solved in injection molding of an article having a fine-pitch net structure, for example a filter for air conditioner or oil filter, by the one-piece molding: